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In a post he captioned: "From a director who feels like a complete idiot," Carney wrote: "Recently, in a phone interview, the conversation turned to a discussion about a past film, Begin Again, starring Kiera Knightley.

"I said a number of things about Keira which were petty, mean and hurtful. I'm ashamed of myself that I could say such things and I've been trying to account for what they say about me. In trying to pick holes in my own work, I ended up blaming someone else.

"That's not only bad directing, that's shoddy behaviour, that I am not in any way proud of. It's arrogant and disrespectful.

"Keira was nothing but professional and dedicated during that film and she contributed hugely to its success. I wrote to Keira personally to apologise, but I wanted to publicly and unreservedly apologise to her fans and friends and anyone else I have offended. It's not something that I could ever justify and will never repeat (sic)."

Carney blasted the two-time Oscar nominee's acting skills in his recent interview and described his new movie as "a small personal movie with no Keira Knightleys in it".

He said: "I learned that I'll never make a film with supermodels again ... I like working with actors and I wanted to come back to what I knew and enjoy film-making again - not that I didn't enjoy Begin Again, but Keira has an entourage that follow her everywhere so it's very hard to get any real work done ... Keira's thing is to hide who you are, and I don't think you can be an actor and do that ...

"I don't want to rubbish Keira, but you know it's hard being a film actor and it requires a certain level of honesty and self-analysis that I don't think she's ready for yet and I certainly don't think she was ready for on that film."

The critics were even more odd considering Begin Again, a film in which Knightley portrayed a lovelorn singer, received positive reviews, with an 82 per cent approval rating on Metacritic.

However, he faced an immediate backlash and a number of directors, who have worked with the 31-year-old actress, rushed to defend her.

Mark Romanek, who worked on Never Let Me Go in 2010 with Keira, defended the actress on Twitter.